Approximately 1.7 billion people worldwide are asymptomatically infected with Mycobacterium tuberculosis (Mtb). Co-infection with HIV dramatically increases the risk of developing active TB and constitutes a major impediment to global public health. Notably, there has been little basic research toward defining the mechanisms by which HIV modulates Mtb to enter, persist and emerge from a persistent state in the human tuberculous lung to cause active TB disease. We and others have recently discovered that carbon monoxide (CO), generated by heme oxygenase-1 (HO-1), is an Mtb dormancy signal and that HO-1 is necessary for granuloma formation. Further, it has been shown that HO-1 inhibits HIV replication. These findings suggest a key role for HO-1 in control of the TB/AIDS syndemic wherein HO-1 is key regulator of latency and reservoir maintenance. Our long-term goal is to understand the mechanisms by which HIV modulates TB latency and how these mechanisms can be manipulated for therapeutic and prophylactic purposes. The objective of this work is to generate a detailed, mechanistic understanding of the role of HO-1 and host bioenergetics in the context of TB and HIV infection. Our central hypothesis, based on substantial preliminary data, is that HIV causes an imbalance in the bioenergetic threshold of host cells, which is maintained by HO-1, to shift the balance from latent TB to an active infection. Our rationale is that the successful completion of this proposal will contribute missing, mechanistic elements of HO-1-dependent disease function to our base of knowledge, without which the mechanism of TB latency and HIV-mediated reactivation cannot be fully understood. We will apply novel techniques such as real-time metabolic flux analysis to non-invasively measure the oxygen consumption rate (OCR), extracellular acidification rate (ECAR), spare respiratory capacity (SRC), maximal respiration and ATP turnover of cells infected with Mtb and/or HIV. This powerful technology has not yet been applied to study the bioenergetics of bacterial/viral host interaction. We also will exploit novel HO-1 transgenic animals, and human TB lung tissue to accurately describe roles for HO-1 in TB/HIV in vivo. Further, we will examine the bioenergetic status of healthy, latent TB, active TB, TB/HIV and HIV-infected patients in South Africa. The research is innovative, in our opinion, because it represents a new and substantive departure from the status quo by applying novel technologies and unique patient cohorts to examine HO-1 and bioenergetics as paradigms to better understand TB/HIV disease. This contribution is significant because it is the first step in the continuum of TB/HIV research that will (i) provide in-depth mechanistic insight from a basic and clinical research point of view into the role of HO-1 in regulating HIV and Mtb disease, (ii) characterize the bioenergetic threshold of TB/HIV patients, and (iii) identify the Mtb/HIV co-infected cell populations and cellular events in human lung granulomas. Overall, these studies will provide a new basis for understanding TB and HIV persistence in the human tuberculous lung.